Tokkai Hei 7-139413 published by the Japanese Patent Office in 1995 discloses a control method of a diesel engine equipped with a turbocharger and an exhaust gas recirculation (EGR) device. The EGR device comprises an EGR valve which regulates an EGR flowrate. The control method determines a turbocharging region and an EGR region according to a load and rotation speed of the engine.
"Simulation of a variable geometry turbocharged-diesel engine for control algorithm development", C524/127/97 published by the United Kingdom Institution of Mechanical Engineers (IMechE) in 1997 discloses a control method for controlling the EGR valve and a variable nozzle of the turbocharger in a transient state of the diesel engine.
"EGR System in a Turbocharged Diesel Engine", pp. 193-196, Technical Preprints, published by the Japan Institute of Automobile Technology in October, 1996, discloses control of the EGR flowrate of the EGR device by varying the opening area of the variable nozzle of the turbocharger.